This invention relates generally to rotating disk data storage apparatus, and particularly to that of the hard or "fixed" disk variety. More particularly, the invention deals with an improved system in such apparatus for detecting the servo sectors of tracks on the disk without relying on a disk revolution sensor such as that comprising a frequency generator.
The hard magnetic disk has a multiplicity of annular tracks arranged concentrically on at least one major surface thereof. Each track is divided into sectors each consisting of a data subsector and a servo subsector. The data subsectors are used for the storage of user information. The servo subsectors have written thereon automatic gain control (AGC) data, track data, and tracking servo patterns.
Hard disk drives usually incorporate a disk revolution sensor, as in the form of a frequency generator, which, upon rotation of the disk, produces a series of sector pulses indicative of the servo subsectors of the disk tracks. The revolution sensor is additionally used for constant speed rotation of the disk under servo control.
There are, however, some hard disk drives that dispense with a frequency generator with a view to reduction in size and cost. Such disk drives determine the servo subsectors of the rotating disk by detecting the gaps of predetermined length between the track sectors. Conventionally, errors have been almost unavoidable in such methods of sector detection based upon the intersector gaps as represented by the output waveform of the data transducer. Wrong sector pulses could make it impossible to correctly write and read data on the disk, and undesired destruction of prewritten data could also occur in writing new data.